Present day efforts in the aircraft industry are directed to developing aircraft that can operate at very high or supersonic speeds. Such supersonic aircraft, particularly when used as combat fighter planes, should be highly maneuverable to allow rapid turns, rolls, dives and ascents without danger of stalling or loss of control. Some aircraft may need to cruise long distances at supersonic speeds requiring the most efficient integration of the engine-propulsion system and the external airframe aerodynamics. Also, it is desirable that the aircraft should be capable of performing landings and takeoffs at low subsonic speeds, using a minimum length runway or, for some missions, landing or taking off vertically. To realize these goals for high speed aircraft, it is necessary to have optimum control of powered lift and air flow.
Recent investigations of aircraft configurations indicates that a significant number of benefits may be achieved by utilizing a forward swept wing (FSW) planform. When an FSW is used in combination with a canard at transonic and low supersonic maneuvering flight, favorable interference is provided over the inboard portion of the wing where the shock is strongest. This leads to higher aerodynamic efficiency than with the use of aft swept wings. In an aft-swept wing configuration the spanwise flow normally thickens the boundary layer at the tips. The flow on an FSW tends to separate first at the inboard section while good flow conditions can be maintained at the tip because of low induced angles of attack of the outer wing sections and because the air tends to flow toward the root rather than to the tip as it does on a sweptback wing. These flow conditions result in stall characteristics which allow the ailerons to remain effective at high angles of attack, even after most of the wing has stalled. Thus the FSW aircraft is more controllable at higher lift coefficients. Another benefit is a geometric advantage when the FSW is utilized in an STOVL aircraft. A conflict in the positioning of wing box and the portion of the power system providing vertical thrust can produce problems with the fineness ratio, overall length, and area ruling. On a sweptback wing most of the root chord must be positioned at the center of gravity which conflicts with the positioning of the vertical thruster in any STOVL configuration. For the FSW, the root of the wing (containing the wing box) is located behind the center of gravity. FSW aircraft are described, for example, in DARPA Report 8709-80-TR-73, "Second Assessment of Forward Swept Wing Technology," March 1980.
Notwithstanding the above-mentioned attributes, because the FSW aircraft tends to stall first on the inboard wing sections rather than on the outboard sections, the inventors have found a need for additional flow or stall control in FSW aircraft when operating in low speed flight experienced during takeoff and landing as well as at high angles of attack. Further, there is a need for an improved FSW that can operate at high subsonic and moderate supersonic speeds (M, 1.5-3.0) and exhibit either or both good maneuverability and efficient sustained cruise flight characteristics.